I think we're ready now to
tackle some more, or even more complicated examples. So let's draw
something crazy here. Let me draw a chain. Let me draw it like that. And so like we've done
in all of the examples, you'll want to find
the longest chain. We can count from here one, two,
three, four, five, six, seven, eight. Or maybe it's one, two,
three, four, five, six, seven. No. Or maybe it's 1, 2, 3,
4, 5, 6, 7, 8, 9, 10. That is our longest chain. Let me just make that in green. So our longest chain
here is in green. So this backbone has
10 carbons in it. The prefix for 10 is dec. It is a alkane since it
has all single bonds. So we can write decane
for the backbone. And then it has a
group right here. And this group consists of
one, two carbons attached to the backbone. The prefix for two carbons is
eth, so this is an ethyl group. The y-l is because it's a group
attached to the main alkane chain. So we call this ethyl decane. But we have to specify where
the ethyl group is attached, and we want to give it as
low of a number as possible so we start counting on
the side closest to it. So it's one, two,
three, four, five. So this is 5-ethyldecane. Now let's complicate
this a little bit more. So let me just copy
and paste this. So I have pasted it there, and
let me complicate this molecule a little bit more. Let me add another
ethyl group to it. So let's say we have another
ethyl group over there. Now what is this going to be? Well the longest
chain is still going to be that thing in green. So it's still going
to be a decane. But now we have
two ethyl groups. One on the five carbon,
one, two, three, four, five, and then one on the six carbon. You might be tempted to write
5-ethyl 6-ethyldecane, which really wouldn't be
wrong, but it would just be maybe more letters
than you want to write. Instead you write 5
comma 6-diethyldecane. The 5, 6, tells us the two
carbons on the main backbone that the ethyl groups
are attached to, and the di says that we have two
ethanes, or two ethyl groups I should say, not ethane
groups, two ethyl groups, one over here, and one
right over here.